Changeset 10813

From Colin MacDonald?, "In my application I have a custom graphics context class, derived from
osg::GraphicsContext?, in order to give good integration with the
application's GUI toolkit. This works really well.

However, I need to share OpenGL texture resources with the standard
osgViewer GraphicsContext? implementations, in particular the PixelBuffers?. This is essential for my application to conserve graphics
memory on low-end hardware. Currently the standard osg implementations
will not share resources with another derived osg::GraphicsContext?,
other than the pre-defined osgViewer classes e.g. PixelBufferX11 is
hardcoded to only share resources with GraphicsWindowX11 and
PixelBufferX11 objects, and no other osg::GraphicsContext? object.

To address this in the cleanest way I could think of, I have moved the
OpenGL handle variables for each platform into a small utility class,
e.g. GraphicsHandleX11 for unix. Then GraphicsWindowX11, PixelBufferX11
and any other derived osg::GraphicsContext? class can inherit from
GraphicsHandleX11 to share OpenGL resources.

I have updated the X11, Win32 and Carbon implementations to use this.
The changes are minor. I haven't touched the Cocoa implmentation as
I'm not familiar with it at all and couldn't test it - it will work
unchanged.

Without this I had some horrible hacks in my application, this greatly
simplifies things for me. It also simplifies the osgViewer
implementations slightly. Perhaps it may help with other users'
desires to share resources with external graphics contexts, as was
discussed on the user list recently."

Notes from Robert Osfield, adapted Colin's submission to work with the new EGL related changes.